Set the alpha mask fixing software rendering in OpenGL

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%403256

src/video/SDL_yuv_sw.c

@@ -939,10 +939,13 @@ SDL_SW_SetupYUVDisplay(SDL_SW_YUVTexture * swdata, Uint32 target_format)
     for (i = 0; i < 256; ++i) {
         r_2_pix_alloc[i + 256] = i >> (8 - number_of_bits_set(Rmask));
         r_2_pix_alloc[i + 256] <<= free_bits_at_bottom(Rmask);
+        r_2_pix_alloc[i + 256] |= Amask;
         g_2_pix_alloc[i + 256] = i >> (8 - number_of_bits_set(Gmask));
         g_2_pix_alloc[i + 256] <<= free_bits_at_bottom(Gmask);
+        g_2_pix_alloc[i + 256] |= Amask;
         b_2_pix_alloc[i + 256] = i >> (8 - number_of_bits_set(Bmask));
         b_2_pix_alloc[i + 256] <<= free_bits_at_bottom(Bmask);
+        b_2_pix_alloc[i + 256] |= Amask;
     }
 
     /*